1. Field of the Invention
The present invention concerns the field of devices for measuring the level or the volume of a liquid contained in a reservoir.
The present invention, more precisely, concerns a device for measuring the level or the volume of a liquid contained in a reservoir of the type comprising a casing that houses an element defining two generally vertical, separate electrical tracks, at least one of which is electrically resistant; and a float capable of following the level of the liquid, which bears a slider capable of connecting the two tracks.
The value of the resistance measured between the two ends of the tracks directly represents the above-mentioned level and/or volume.
2. Description of the Prior Art
Many devices of the type indicated above have already been proposed.
The documents FR-A-2 550 338, FR-A-2 503 861 and FR-2 534 375 describe exemplary embodiments of these devices.
The problem that arises is of designing measuring devices of the type indicated above having a substantial depth, for example, a depth of more than one meter.
As the element defining the two electrical tracks is generally made with elongated strips punched into a printed circuit, which strips consequently have poor mechanical strength, it appears to be necessary for devices of substantial depth to have spacers for reinforcing purposes between the element defining the two tracks and the casing.
However, since for reasons of sensitivity, equilibrium and cost, the float has to be made in the form of a ring-shaped body surrounding the above-mentioned element, the spacers hinder the movement of the float all along the height of the tracks.
To try and remove this drawback, subsequent to research and as shown in the appended FIG. 1, the Applicant has considered the superimposition of several devices known in the prior art, each comprising two conductive tracks and one float placed respectively on either side of spacers, and the series connection of the corresponding tracks.
In the appended FIG. 1, reference numbers 10, 20, 30 have been assigned to three known superimposed devices shown schematically here. The device 10 has two tracks 11, 12 and a float bearing a slider 13. The device 20 has two tracks 21, 22 and a float which has a slider 23. The device 30 has two tracks 31, 32 and a float which has a slider 33. The connections that serially connect the tracks 12 and 21 and 22 and 31 are referenced 40, 41. The above-mentioned spacers are placed between the devices 10, 20, 30 to physically separate the floats of each device. These spacers re not represented in the schematic illustration of FIG. 1.
Following tests, it has proved to be the case that the arrangements shown in FIG. 1 provide a theoretical solution to the above-mentioned problems, but are not entirely satisfactory in practice.
Firstly, the devices shown in FIG. 1 require the presence of conductive connections 40, 41 on the elements 10, 20, parallel to the tracks 11, 12 and 21, 22 respectively. The width and the cost of the corresponding elements are therefore substantially increased. Secondly, in certain configurations, it is possible to find six slider/track contact resistors in series, and this greatly disturbs the measurement.